Contemporarily, pulverulent materials are transported in and discharged from tank vehicles, the discharging being effected through a closed system to minimize contamination of the atmosphere by dust. When discharging powdered materials such as cement, discharge is greatly facilitated if the material is aerated or fluidized before entering the piping system through which the product is pneumatically conveyed. The vehicles may be in the form of elongate, substantially horizontal tanks with one or more discharge hopper devices along their lower side to which the product may migrate by gravity to the pneumatic conveying piping system, a portion of which may be carried by the vehicle itself. The interior of the tank may be pressurized to facilitate the discharge, and as above noted, the discharge is greatly facilitated if the material is aerated or fluidized before entering the pneumatic conveying pipe system. A common means of achieving fluidization is the use of porous or similar elements through which air is introduced into the hopper of the tank whereby fluidization of the material adjacent the discharge mouth is effected thereby to assist in conveying the material to the discharge port. These porous elements or pads exhibit certain undesirable characteristics, in particular their propensity to blinding due to the fact that the air passed therethrough normally contains a certain amount of foreign material or dust which gradually fills the pores of the material (i.e., canvas). Also, these porous pads make it difficult to clean the hopper assembly.
However, without some form of aid, bulk products such as cement when discharged through the narrowed hopper outlet mouths tends to pack or bridge at these outlets and it is therefore relatively essential that some means be provided to aid in this discharge.